dd_rhelp is a bash script that handles a very usefull program written in C
by Kurt Garloff which is called dd_rescue, it roughly act as the dd
linux command with the caracteristic to NOT stop when it falls on read/write
errors.
This makes dd_rescue the best tool for recovering hard drive having bad
sectors. (dd_rescue can be found here:
http://www.garloff.de/kurt/linux/ddrescue )
But using it is quite time consuming. This is where dd_rhelp come to help.
In short, dd_rhelp will use dd_rescue on your entire disc, BUT it will
try to gather the maximum valid data before trying for ages on bunches of
badsectors. So if you leave dd_rhelp work for infinite time, it'll have the
same effect as a simple dd_rescue. But because you might not have this
infinite time (this could indeed take really long in some cases... ),
dd_rhelp will jump over bad sectors whenever it encounters too much in a
row. In the long run, it'll parse all your device with dd_rescue.
You can Ctrl-C it whenever you want, and rerun-it at will, it'll resume it's
job as it depends on the log files dd_rescue creates.
In addition, progress will be shown in a ASCII picture of your device beeing rescued.
As stated by Kurt Garloff for his dd_rescue program: "Just one note: It
does work. I unfortunately did not just create this program for fun ..."
dd_rhelp goes the same as it has saved me YEARS on my hard drive.
For some times, dd_rhelp was the only tool (AFAIK) that did this type of
job, but since a few years, it is not true anymore: Antonio Diaz did write a
ideal replacement for my tool: GNU 'ddrescue'.
Yes, this is not very clever to have called a tool the same name that
dd_rescue from Kurt Garloff (catch the subtle difference between 'ddrescue'
and dd_rescue ?), but it seems that it was done by intent as we warned
Antonio Diaz from the fact it would probably mess users in this tiny world of
hard drive recovery tools.
Nevertheless, I really encourage you to use this replacement tool if it works for you (and it should be the case). Why ? Understand first what we are comparing:
dd_rhelp(in dirty bash script) +dd_rescue(in C) in one hand- ddrescue (in C) in the other.
dd_rhelp was meant as a quick hack to implement what dd_rescue didn't
do, and what couldn't be done at that time (AFAIK).
It could be some cases where ddrescue won't work, and this is the major reason
why I keep maintaining dd_rhelp. It is important to tell me and Antonio Diaz
when these cases occur.
Now that you are enlightened, you are free to use dd_rhelp.
Well, you do not WANT to use dd_rhelp. I hope you'll never HAVE TO use it.
Basically, if you have bad sector corrupting your filesystem you'll have several solutions depending on the filesystem itslef, the partition table, and what remains accessible...
In some recovering process, as a first stage, you'll need to secure all the remaining data of your disk (or partition) in a file or partition on a healthier device. Often, next operation is to fsck.* your recovered data to rebuild the damaged filesystem information. Whith chance, you will be able to mount the result and access files. These could then be in various states depending of how they have been affected by the damages. Possible file states are ranging from completely recovered without any further work, to lost, damaged, scrambled, and often anonymously collected in your filesystem lost+found directory...
dd_rhelp and dd_rescue are meant to be in the very first phase only:
securing your remaining data into a another file.
dd_rescue which has been created by Kurt Garloff, is a great program. And
could already help you without dd_rhelp. But in some case, like disks
cluttered with bad sectors, it can be time consuming to use for 2 main reasons:
1. it does straight recovery, and thus can spend months making it's path in a solid bunch of bad sectors before rescuing hole portions of perfectly sain data hidden just after.
2. if you decide to manoeuver
dd_rescueto stop him when he's bumping in large sequences of bad sectors and try to start it from spots to spots in normal or reverse direction (asdd_rescueoptions allows this), then this can require a lot of YOUR time.
It is where dd_rhelp comes to help: it is a wrapper for dd_rescue. This
means it'll call it with various arguments to change it's start position or the
direction of the scanning process. It'll guide dd_rescue into a new
behavior which will lead to rescuing much more data in the beginning of the
process all over the disk.
If you didn't really understood, here's another explanation :
This can really take a long time if you have much bad sectors. (and I had this problem).
As bad sectors tends to be in large groups and these groups seems to tend to be
dispatched on drive, and if you just launch dd_rescue on the beginning of
your drive and there is a large group of bad sectors coming next, you could be
waiting for years before rescuing any data. While waiting, your anxiety will be
free to grow as you won't have answer to these dreadful questions: - Is there
any valid data to rescue AFTER this chunk ? - How big is this chunk ? - When
will I get answer to these two first question ?
So your solution with dd_rescue is to stop dd_rescue, and "jump" ahead
randomly and try to copy from a chosen offset. Then you could again fall on a
group of bad sectors... and then you should stop dd_rescue and jump
somewhere else on your drive. This behavior involves the user's constant
presence (you !).
The idea of the dd_rhelp shell script is to do this job: launching
dd_rescue for you on the disk while trying to get the max amount of data
out of your disk in a minimum of time. It'll be jumping over bad blocks, using
the reverse copy option of dd_rescue to pin out bad sector group and rescue
as much data as you could have rescued manualy.
This is a good question. dd_rhelp uses dd_rescue to compute a recovery
path through the device that will focus on valid data recovering. This recovery
path will go through all the device, exactly as dd_rescue could do it on
its own without any path. This means that dd_rhelp will save you time ONLY
IF YOU INTEND TO CANCEL ITS JOB BEFORE THE END of a full recovery.
Why wouldn't you want a full recovery ? because a considerable amount of time is taken to try to rescue badsectors. This amount of time can be mesured in days, month, years, depending on your device capacity and its defectiveness. You might not want to spend this time knowing that 99 percent of this time will be taken to look at badsector and won't lead to any more data recovering...
dd_rhelp shifts this useless waiting time to the end of the process. Using
dd_rescue straight throughout your device make waiting time dependent on
the badsector distribution.
Think about dd_rescue standalone if you only intend (and can afford) to
wait until a full dd_rescue scan. dd_rhelp optimizes only the order in
which this full scan will occur to focus on recovery of what will be
recoverable in first. So in the end, launching dd_rhelp for a full scan
will take exactly the same time dd_rescue would have taken plus a
considerable time which correspond to the overhead of calculating its path.
This shell script is very basic and not well written, but it supports the "--help" and "--version" of GNU Coding Standard. It should be quite straight-forward to use.
so go for a:
dd_rhelp --version
When running dd_rhelp you can safely Ctrl-C, or kill dd_rhelp, it'll
resume its job the next time you call it.
Olivier SANTIANO, a french dd_rhelp user shared his experience of complete
process of recovering his hard drive with dd_rhelp and post-dd_rhelp
recovery work: http://f1efq.free.fr/save.htm (in french)
Since 0.1.0, dd_rhelp is directly usable (you can copy it to a directory in
your path, or use it directly out of the box).
dd_rhelp uses log files made by dd_rescue. Precisely, it searches for
the "Summary report" that dd_rescue prints when its job is over.
1.
dd_rhelpcreates itself an internal representation of what has been parsed withdd_rescue.2. It'll find the greatest part of the disk that hasn't been tested and will launch
dd_rescuefrom the middle of this part backwards, then forwards until it rescues without error all data, or until it falls on 5 consecutive read errors.3. Go back to step 1 unless everything has been rescued with
dd_rescue...
It worked fine for me (home made distrib) on big harddrives (partitions of 15 Gigs). Received positive feedbacks on large partition (60 Gigs and 200 Gigs), and it should only be limited by the linux kernel limitation. Though the bash script could be longer to compute next position in very large disk with lots of bad sectors scatered all over your disk.
It worked on Debian, Ubuntu, and on a Knoppix CD. After each release, I test it on a knoppix with a 1.44M diskette with badsectors or a damaged CD-ROM/DVD-ROM.
Darwin/MacOSX should be supported. This support is erratical, so more feedback are appreciated.
If you have any other experiences of dd_rhelp, please let me know.
Note
This shell script needs version >= 1.03 of dd_rescue ! And was
tested with all version up to 1.28.
The source code is on github. Feel free to fork it and start hacking around, I'll be gratefull to receive some pull requests.
You should also note that dd_rhelp code is separated in 2 parts:
- the libraries that are in the beginning of the file
- the actual
dd_rhelpcode which is at the end of the file
The library are actually included when I have to create a new package. They are
accessible on a different repository than dd_rhelp code itself. These library
are called kal-shlib-*.
kal-shlib-common contains the code included in dd_rhelp.
kal-shlib-pretty, kal-shlib-shunit, are the repositories for the libraries
used (and included) in dd_rhelp.test, the unit test file.